Various synthetic and naturally occurring water-soluble polymers have been developed which exhibit excellent thickening and flocculating properties. Most commonly used are acrylamide polymers which include poylacrylamide and its water-soluble copolymeric derivatives such as acrylamide-acrylic acid and acrylamide-acrylic acid salt which contains 95-5 percent by weight acrylamide. Copolymers of acrylamide with vinyl monomeric such as maleic anhydride, acrylonitrile, styrene, and the like are also useful. Other useful water-soluble vinyl polymers are described in detail in U.S. Pat. Nos. 3,418,237; 3,259,570; and 3,171,805. The polymers are generally available in powder form but useful only when dissolved in water.
One method of use has been to first disperse the polymer in a carrier such as oil. The polymer is generally highly concentrated in the carrier and must be diluted to a concentration of approximately 8%-10% in water or other diluents before use. One such method using a oil based carrier is disclosed in U.S. Pat. No. 3,624,019.
The polymers have molecular weights of up to 25,000,000. As such, they exist in the carrier in tight coils. The active sites for treatment of wastes are believed to be along the chain and in the coil form the polymers are not effective. In addition to being diluted, the polymers must also be allowed to uncoil to expose the active sites and activate the polymer.
Due to the size and length of these polymers, they must be mixed gently to prevent breaking up of the chains into smaller, less efficient particles. There is, therefore, presented a problem in the mixing and dispersion of polymer in diluent. If the polymer becomes uncoiled during mixing, it can be broken up. Methods and apparatus have been designed to disperse the polymer gently in water--see for example U.S. Pat. No. 4,522,502. Also my U.S. Pat. No. 4,747,691 mixes first then activates the polymer after mixing in an unagitated aging tank.
Drawbacks to both the above patents exist, in that mixing and aging times are not set out with particularly. For example, in my patent, the aging tank and mixing tank have substantially the same residence time. I have since discovered that this is not sufficient to get the best results from the polymer. Data indicate that the diluted polymer should not be agitated more than 30-45 seconds and should be aged for approximately 2-10 minutes. I have thus improved upon my earlier invention by providing an apparatus which provides the required mixing and aging times.